Ponting got an inside edge, but it was very, very slight and it's unsurprising that the umpire missed it. Martyn's, however, was really quite thick and should have been picked up by a first class umpire. If I'm not mistaken, it was Martyn that was at the end of a very similar decision in the previous test.
Hell, who am I kidding? We're smashing the Aussies! \o/ Hurrah for glued-on bails, too. ;)